Method for treating selected formations penetrated by a well



CRQSS REFERENQE SEARCH RGDN 'NOV- 26, 1963 R. w. DAVIS EI'AL 3, 88

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" ROBLEY W. DAVIS v vJOHN H. WAGNER INVENTORS ATTORNE Y Nov. 26, 1963 I R; w. DAVIS EIAL umaon FOR TREATING SELECTED FORMATIONS PENETRATED BY A WELL 2 Sheets-Shet 2 Filed larch 4, 1959 FIG 7.

ROBLEY W. DAVIS JOHN H. WAGNER INVENTORS ATTORNEY United States 3,111 988 METHOD FOR TREATIN G SELECTED FORMA- TIONS PENETRATED BY A WELL Robley W. Davis and John H. Wagner, Vivian, La., as-

This invention relates to an improved process for increasing the recovery of fluid from a well. More particularly, this invention pertains to a process for hydraulically fracturing orotherwise injecting a treating fluid into selected formations penetrated by a Well,

In the hydraulic fracturing process, a low-pentrating fluid is injected into a formation at high rate to produce a fracture which desirably extends into the formation for a great distance to thereby increase the effective permeability of the formation affectedby the fracturing process to fomiation fluids so that those fluids flow into the well more easily. In the process as applied to open-hole completions, i.e., to fracturing or otherwise treating a formation in the open hole below the casing, it has been shown that since a greater pressure is required to initiate a fracture than to extend that fracture into the formation, normally only one fracture is produced; and unless all previously produced fractures are at least temporarily plugged, it is improbable that a new fracture can be initiated. When wells are completed with the casing set through the producing formation or formations, the casing is typically perforated throughout each producing zone with about three or four perforations per foot. The casing opposite each producing formation may thus be perforated either by jet or bullet perforators with as many as a hundred or moreholes, depending upon the thickness of the producing formation. It has been found that when a cased well has been completed by this procedure, the productivity increase or fracture-efficiency is often less than in the case of an open-hole completion. It is apparently impossible to extend a fracture into a formation behind a casing to as great a depth as can be attained in open-hole completions. As a partial explanation for this difference,

it has-been found that each perforation has a limited flow capacity. When liquid flow through a perforation reaches its critical velocity, flow through that perforation cannot be further increased; it is flowing at capacity.

If the pump capacity is greater than the capacity of the perforations receiving fluid, another perforation is broken down and 1 commences to take the treating fluid.

' tend the fracture into the formation to as great a depth as can otherwise be attained in an open-hole completion. This low fracture efficiency is thus attributed to the excessivenumber and wide spacing of the perforations which may take the injected fluid and the fact that with such wide spacing, the fluid discharged through the various perforations does not combine and produce a single fracture. t short, it has been found that by first perforating the casing with a great number of widely spaced holes which are spread ove r agreat vertical distance, the perforations are generally in communication behind the pipe, and that due to the limited capacity of each perforation and the lack of communication between perforations behind the pipe, several fractures may be produced simultaneously in one or more formations behind the pipe. The rate of fluid injection into each fracture is therefore lower than desirable and, consequently, assuming a fracturing liquid which leaks away to some extent intothe formation, thi: ability to atom:

paratus for fishing the extend each of the fractures into the formation is some? "an improved method for injecting a treating fluid into selected formations penetrated by a well. It is a more specific object of this invention to provide a process wherein the formations penetrated by a cased well can be fracturcd with one or more deep-penetrating fractures. It is still a more specific object of this invention to provide an improved hydraulic fracturing process for Wells which have been completed with the casing extending through the producing formation and perforated in a producing zone wherein the fracturing efliciency is increased by use of a free packer to limit the number of easing perforations which can take fluid at, any one time and by grouping or concentrating those perforations which can take fluid at any specified time sothat they are all in communication behind the casing. Another object of this invention is to provide a free packer which is particularly adapted for use in our improved process. Other. objects of this invention will become apparent as the process is further described hereinafter and by reference to the accompanying drawings in which:

FIGURE 1 is a cross-sectional view of=a well showing suitable apparatus for carrying out the steps of our process;

FIGURES 2-6 are cross-sectional views of the Well shown in FIGURE 1, showing in sequence the steps of our preferred process;

bodilment of our free packer; and

'FIGURE 8 is a cross-sectional view of anvauxiliary apfree packer shown in FIGURE 7 from a well. In brief, this invention may be described as a' well completion process in which a treating fluid is selectively injected into a particular formation penetrated by a well after lower formations or sections of the same formation have been treated by isolating the treated section of the well with a free packer-as the fluid is injected into the selected formation. In its more specific aspects, fractures are produced in a cased well by first temporarily plugging existing perforations and fractures with a free packer, then making a multiplicity of higher casing perforations concentrated in a short section of the casing so that the perforations are in fluid communication behind the pipe, and then injecting a fracturing liquid into the. well at .a high rate and at a high pressure to fracture the formation at the elevation of the upper perforations; with a single deep-penetrating fracture. As. applied to producing multiple fractures in a cased Well, a first formation fracture or set of fractures is initiated and extended into a formation as desired by pumping a fracturing liquid at high rate into that formation through perforations at a low elevation in a well. formation at a higher elevation in the same well is then fractured by plugging the mouth of the first fracture or set of fractures with a free packer, then making a number of additional casing perforations, concentrated within a short section and above the first perforations, and then injecting another quantity of fracturing liquid into the well at a high pressure and at high rate while the mouth of the first fracture or set of fractures is plugged by one or more free packers so that a fracture is .inititated at The same formation or another.

- even through the lower producing formation 13.

are retrieved by fiowtion 13. These producing formations are separated by an impermeable nonproductive zone 14 and are therefore, but for the well 10, not in fluid communication with each other. In situations like this the well may either be dually completed, i. e., the production from each zone may be kept separate, or production from these two zones may be commingled in the well. Casing 15', often referred to as the producing string, extends from the surface down through the upper producing formation 12 and into or It is typically cemented in the well by pumping cement up around the casing between the well wall and the casing to an elevation above the top.producing formation 12 so that the upper and lower producing formations. are not in fluid communication through the well behind the pipe in the nonproductive zone 14. The casing is then perfoplicity of holes, e.g., 4-10 or more, are produced preferably simultaneously in a ring around the pipe. Several of these multijet perforators spaced vertically as close as possible may be employed so that as many as 15-30 or more holes may be produced in the casing within a vertical space of a foot or less. The lower producing formation may then be produced through this first set of perforations or a first or bottom fracture may be produced therein by injecting fracturing liquid through the perforations so that the productivity of formation 13 is increased.

When itis desired to complete the well in the upper producing formation 1'2 special well head or surface apparatus is installed at the upper end of the casing 15. This surface apparatus includesa lubricator 18 on the upper end of and substantially the same diameter as casing 15 and means including a stuffing gland 19 to close the upper end of the lubricator. A lubricator which may include valves, as is well known in this art, is particularly desirable where the well is under superatrnospheric pressure. A casing perforator 21 is suspended in the upper end of the lubricator above the lubricator inlet 22 by a wire line 23 which extends through the stufling gland 19. This casing perforator has a number of circumferentially disposed jet charges 24 around its periphery with the jets directed outwardly so that when the casing perforator is detonated, it will produce a number or set of holes in the casing all at about the same elevation and preferably in a ring. A high-pressure, high-volume pump 25connected to a treating fluid supply (not shown) by suction-"line 26 discharges a well treating fluid such as acid or a low-penetrating fracturing liquid into the well through flow line 27, valve 28, and casing inlet 29. A bypass line 31 connected to the pump discharge between pump 25 and valve 28 delivers treating fluid to the lubricator inlet 22 when bypass valve 32 is open. A free packer 33, i.e.,

a packer which may be run into and withdrawn from the well hydraulically and without a mechanical connection, is disposed in lubricator 18 below perforator 21. Basically this free packer consists of a mandrel 34 on which is mounted an upper cup-type packer element 35 with the open end turned down and two lower oppositely disposed cup-type packer elements 36 and 37. The centel packing element 36 has the open end turned up and the bottom packing element has the open end ttirned 4 down. The upper packer element is primarily for lifting the free packer out of the well with the rising fluids when the well is produced. "The lower packer elements, which may be joined or butted together, as indicated, or spaced as desired to span any lower casing perforations or permeable zones in an open hole, prevent treating fluid injected into the well above the free packer from entering the formations spanned.- A 'pin 38 through the wall of the lubricator supports the free packer and prevents it from falling prematurely into the well below the casing inlet 29. 1

After the lower perforations 16 have been made in casing within the lower producing formation 13, and

- the apparatus has been thus assembled, a first quantity of fracturing liquid 39, preferably having granular props such as sand 41 suspended therein, is pumped into the well and through these perforations to produce a first fracture 42. The sand is deposited in this fracture, asis well known in the art, to prevent the fracture from collapsing after pressure is removed and to thereby maintain a highly permeable fracture.

The quantity of fracturing or other treating liquid. and the rate of injection thereof may be varied over a substantial range depending upon a number of elements including the area of fracture desired. The rate offlinjection of the fracturing fluid is. desirably correlated with the size and number of perforations 16. A typical perforation through casing' and the material behind the casing,

i.e., a perforation %'--/2 inch in diameter, has a flow'capacity at the critical velocity of from about 1 to about 1% barrels per minute. Even with a substantial increase of pressure within the casing, the flow rate cannot therefore be materially increased. Since the viscosity of the fluid and the size and shape of perforations often vary considerably from the average, in some cases it is'desirable to determine beforehand by surface tests the flow capacity with the particular treating fluid of the perforations produced with'the perforator to be used in perforating the well casing. Knowing the fiow capacity of each perforation, the desired number of properly grouped holes can be shot in the casing more efliciently to utilize the capacity of pump 25. I

After the desired quantity of fracturing liquid has been injected into the well, the suction line 26 of pump 25 is connected to a supply of follower fluid which is typically a solids-free or clean fluid, such as oil or water, and this follower liquid 43 which may form an interface 44' with the fracturing liquid displaces the fracturing liquid down the well and into the first 'formation fracture 42. At about the time the first of the follower liquid is discharged into the casing via casing inlet 19, the pin 38 is removed from below the free packer, allowing it to fall out of the lubricator. If, as is'usually the case, the cuptype packer elements aretoo tight in the lubricator to permit the free packer to fall, valve 28 is closed and .bypass valve 32 is-opened so that the free packer is forced out of the lubricator and carried by the follower liquid down the well. to perforations 16, as indicated in FIG- URE 3, with cup-type packer elements 36 and 37 spanning and closing the perforations. The surface pressure will then reflect a sudden increase in pressure, giving an indication that the perforations are sealed or the bottom of the well spanning any permeable zone in the well is plugged.

It is an important element of this invention that any other formations or sections of formations which are to be treated via this same well, are treated while these and all previously produced perforations and fractures are sealed or plugged. Therefore, while the first or all previously produced perforations are plugged, casing perforator 21 is lowered into the well on wire line 23 to a position in which the charges 24 are at the elevation in the upper producing formation 12 at which the casing is to be perforated. The second set of perforations 46 is then made in the casing at the desired elevation by detonating the charges 24. The perforator is withdrawn from the well into the lubricator 18 above the casing inlet 19 or otherwise removed from the well. The pump suction 26 is again connected to the fracturing liquid supply and a second quantity of fracturing liquid 47 is injected into the well. It may form an interface or a short mixing zone 48 with the follower fluid 43 as it displaces that follower fluid into the upper producing formation 12. The second quan tity of fracturing liquid then enters the upper producing formation through the second set of perforations 46 and produces a second fracture 49 in the upper producing formation, as indicated in FIGURE *5. As in the case of the first fracture, the, quantity of fracturing liquid injected into this second fracture and the rate of injection may also be varied over a wide range. The rate, however, is as indicated previously, preferably correlated with the capacity of pump and the number of open; perforations to ob tain maximum efliciency. After the second fracture 49 has been extended the desired distance into the upper producing formation l2, the fracturing liquid remaining in the well may be displaced into that fracture by again connecting the suction of pump 25 to the supply of follower fluid and injecting a second quantity 51 of this follower fluid into the well. These two fluids may also form an interface or short mixing zone 52 in the well which is displaced by the follower fluid down to the elevation of the second fracture and, if desired, some of the second quantity offollower fluid maybe injected into the second fracture. 1.

While the process has been described by reference to two producing formations and the creation of one fracture in each, it is apparent that the same apparatus and pro-,

cedure can be employed to form any number of fractures in any number of formations provided only that the first fracture is desirably near the bottom of the well or treated formation and any subsequently produced fracture is above previously'produced fractures. Regardless of the number of fractures, when another fracture is to be formed, an important element is that all fractures previously produced be plugged and that in the case of a cased well or producing fonmation, the casing bgigperforated only over a narrow zone at the elevation where the next fracture is to be formed.

In carrying out the process of the present invention, the first packer 33 will tend to stop its descent immediately after the lowermost cup-shaped member thereof passes fracture 4-2. Beneath the aforesaid cup-shaped member, and extending to the bottom of the well, is a column of incompressibleliquid. This column, therefore, serves as a firm base on which packer 33 rests. When it is desired to carry out, for example, a third fracture in a well, a second packer will be inserted therein, as taught, and it will push fracturing liquid ahead. The packer continues to pass on down the well so long as fracturing liquid is taken in through perforations 46(FIG. 4). Such liquid continues to flow into perforations 46 until the lowermost cupshaped member of'the second packer passes perforations 46. At that instant, the movement of the .second packer down the well is halted by the fact that it has come to rest on a second colunm of incompressible liquid between the first and second packers. The second packer, of course, serves to plug perforations 46 and, hence, any subsequent amounts of fracturing fluid introduced into the well under pressure will pass through perforations made opposite the third zone to be fractured. This operation is carried out until fracturing or parting of said third zone-has been obtained to the desired degree.

After the last fracture has been created, as indicated in FIGURES 5 and 6, the well is produced by flowing it through the casing. As liquid from each of the producing formations 12 andf13 commences to flow into the well, i.e., as the pressure differential across the perforations is reversed and the pressure in the formation becomes greater than the pressure in the well, the free packer is diswith the lubricator 18 or it may be displaced from the casing and the lubricator by removing the stuffing gland l9 and flowing the well through the lubricator. In case the well does not flow, a fishing line may be connected to the spear 53 and the free packer lifted from the well.

As indicated above, the free packer may take various forms. An alternative and preferred type'of free packer is shown in FIGURE 7. In this embodiment the packing element 61 may comprise an elongated elastic cylinder or sleeve axially mounted on a tubular mandrel 34' with concavities or cups 62 in the ends so that the ends form expandable seals with the casing or well walls and prevent fluid flow in the well in either direction past the free packer. While the packing element is shown as a single unit, it may obviously comprise two oppositely disposed cup-type packers with their bases together or spaced any desired distance. The length of the packing element in either case is preferably greater than the spacing of the casing perforations or other permeable zones in an open hole which the packer is to plug. In one embodiment the I lower end of a well is plugged or packed off to an elevation above all perforations or permeable areas in the well well, the upper end of the free packer packing element 61 is held at said elevation and the free packer spans the formation to be packed off.

The packing element is mounted on the tubular mandrel 34 and held in position'between a shoulder 64 and the lower end of mandrel extension 65 which is connected as by threads or the like to the upper end of the mandrel. Guides 66 may be fixed on the lower end of the mandrel to align the axis ofthe free packer with the axis ofthe well and prevent wear on the packing element.

The mandrel extension 65 has an axial hole 67 therethrough which is threaded internally near the lower end. The hole is plugged by a threaded plug 68. This plug has an upper splined end 69 so that it maybe rotated by a tool or socket 71 which is run into the well with a fishing tool 72 on a tubing'73. This plug, when installed as shown, prevents fluids from bypassing through the free packer but, when removed, permits fluids to bypass through the free packer so that the free packer can be' withdrawn or fished from the well without swabbing all of the liquid from the well.

In operation our preferred free packer, with plug 68 installed as shown, is pumped into a well in the manner described above. It is carried down with the treating fluid until the lower end 63 strikes an obstruction such as the bottom of the well or until the bottom ,end 74 of the packing element 61 covers the lowest casing perforation or other permeable zone in the well wall. In either case the upper end 75 of the packing element is spaced to plug the well to an elevation above and span the bottom perforations or other permeable zones which take treating fluid to the exclusion or substantial exclusion of an upper zone that is to be treated. Where there are widely spaced permeable zones in a well, it is sometimes desirable, rather than employing a long ttjibular mandrel, to inject several free packers into the well with the packing element on each spanning a separate set of perforations.

After the lower permeable zones in the well are plugged,

upper zones may be treated or perforated and treated as the free packer is removed by fishing. The fishing tool 72 is run into the well on the tubing as described above. The socket 71 extends out of the lower end of the fishing tool and is guided by the bevel 76 on the upper end of the mandrel extension into engagement with the upper splined end 69 of plug 68. The tubing is then rotated to unthread the plug. The unthreaded plug drops to the bottom of the tubular mandrel and is caught in the par tially closed lower end 63. This provides a fluid bypass through the free packer so that when the fishing tool is .1 lowered down over the upper mandrel extension 65 and the free packer is raised by the biting of slips 78 into the upper mandrel extension, the fluids above the packing element 61 will flow through the hole 67 back into or down the well and will not be lifted with the free packer and fishing tool. Upon removal of all the well plugsor free packers, each of the treated formations can be produced through the well in the usual manner.

. From the foregoing it can be seen that various types of apparatus can be employed in our process and that the process as described is susceptible of a wide variety of-variations. 'This invention should, therefore, be construed not to be limited by the above description, but should be construed to be limited only by the scope of the appended claims.

, We claim:

1. A process for treating a first formation in a well tion, comprising the steps of disposing in said casing a freepacker long enough to span and plug all of said perforations and large enough to form a fluid-tight seal with said casing, injecting into said well a first fluid to forcesaid free packer down said well and plug said perforations, after said perforations have been plugged by said free packer, perforating said casing opposite said first formation subsequently injecting a treating fluid into said first formation, and then flowing said well to remove said free packer from said well. r

' 2. A process for-selectively treating an upper geological formation and recovering fluids from the latter, said formation being penetrated by a cased well which also penetratesa lower formation, said well having sufficient incompressible liquid standing in the lower portion thereof to reach said lower formation, comprising perforating said casing opposite said lower formation, disposing in said well a free packer long enough to span the perforations opposite said lower formation and large enough to form a fluid-tight seal with said well and seal off said lower formation, injecting fluid into said well to displace said free packer down said well and seal off said perforations opposite said lower formation from fluid communication with the remainder of said well including said upper formation, perforating said casing in said upper formation, then injecting fluid into said upper formation, and recovering natural and injected fluids from said upper formation via perforations opposite said upper formation.

3. A process for selectively treating an upper formation penetrated by a cased well which also penetrates a lower formation comprising perforating the well casing in said lower formation, disposing in said well a free packer long enough to span the perforations in said casing opposite said lower formation and large enough to form a fluid-tight seal with the well casing between said lower formation and said upper formation, injecting fluid into said well to displace said free packer down said casing past said upper formation and to the level of 'said lower formation to seal off said lower formation casing perforations, perforating said casing at the elevation of said upper formation, and injecting a formation-treating fluid into said upper formation through the perforations in said casing.

4. A process according to claim 3 including flowing said well after injecting fluid into said upper formation to remove said free packer from said well.

5. A process for selectively treating an upper formation and a lower formation penetrated by a cased well,

. said well having sufficient incompressible liquid standing in the lower portion thereof to reach said lower formation,

comprising perforating the well casing in said lower formation, injecting a treating fluid into said lower formaformation casing perforations.

6. A process according to claim 5 including flowing said well after injecting fluid into said upper formation to remove said free packer from said well.

References Cited in the file of this patent UNITED STATES PATENTS 1,736,117 Granger Nov. 19, 1929 2,168,735 Gilstrap Aug. 8, 1939 2,589,656 Armstrong Mar. 18, 1952 2,672,199 McKenna Mar. 16, 1954 1 2,754,910 Derrick et al. July 17, 1956 2,769,497 Reistle Nov. 6, 1956 2,814,347 MacKnight Nov. 26,1-1957 3,028,914

Flickinger 'Apr. 10, 1962 

1. A PROCESS FOR TREATING A FIRST FORMATION IN A WELL HAVING A CASING THEREIN, SAID CASING HAVING PERFORATIONS OPPOSITE ANOTHER FORMATION BELOW SAID FIRST FORMATION, SAID WELL HAVING SUFFICIENT INCOMPRESSIBLE LIQUID STANDING IN THE LOWER PORTION THEREOF TO REACH SAID LOWER FORMATION, COMPRISING THE STEPS OF DISPOSING IN SAID CASING A FREE PACKER LONG ENOUGH TO SPAN AND PLUG ALL OF SAID PERFORATIONS AND LARGE ENOUGH TO FORM A FLUID-TIGHT SEAL 